The present invention relates generally to an electrically regenerable filter cartridge system. More specifically, the present invention relates to the regenerable self-cleaning filter cartridge system for removing carbon, lube oil and unburned fuel particulates from the exhaust of internal combustion engines. In addition, the present invention relates to a regenerable filter cartridge system for removing particulates from Diesel engine exhaust gases. Further, the present invention also relates to a trap or filter for nitrogen oxide (NOx) to convert such gases to more desirable gases and to purge the exhaust of sulfur.
In the automotive industry, there has been a tremendous concern over the introduction of harmful pollutants into the air which have been generated by vehicle exhaust. Due to the negative health effects of such emissions, the Environmental Protection Agency of the United States has expressed a desire to reduce particle emissions from internal combustion engines. In the United States, the majority of particulate emissions come from Diesel engines on trucks and buses, which have not been regulated as closely as vehicles with gasoline engines.
Various attempts have been made to decrease the particulate emissions from Diesel engines. Unlike with gasoline engine vehicles, existing catalytic converters do not work well with Diesel engines since particulates typically clog these devices since the temperatures within them are too low to effectively burn carbon, lube oil and unburned fuel particles. Other efforts have been made to specifically address the Diesel particulate emissions problem. For example, fired burner systems have been employed to heat a combustion chamber, which receives Diesel exhaust for the purpose of burning the particulates within the chamber at very high temperatures. Such combustion chambers suffer from the drawbacks of high initial cost, high complexity, large size, high-energy consumption and high maintenance cost.
Another prior art attempt is the employment of passive particle filters and configurations to trap the particulates associated with Diesel emissions. These passive particle filters are commonly made from ceramic and metal, for example. These passive particulate filters are inadequate because when the filter fills up with carbon particles, the back pressure within the exhaust increases to such a level which necessitates that the filter be either regenerated in some fashion or replaced entirely. Since replacing the filter is not practical, many types of regeneration have been attempted, including the raising of the temperature of the filter above the combustion point of the carbon particulates in similar fashion to a self-cleaning oven. These prior art methods of filter regeneration include using a fired burner assembly using some type of fuel; raising the exhaust gas temperature by turbo charging the engine or other means; reducing the ignition temperature of carbon particles by adding a suitable catalyst to the fuel or filter material; and electrical heating. The foregoing methods of filter regeneration are not typically used in vehicles today due to their associated cost and practicality.
Further, there have been prior art attempts to employ electrically regenerable filter media instead of the passive filters that need to be replaced and fired burner systems which burn off the collected particulate matter. While the prior electrically regenerable filter media is suitable for burning off collected particulate matter, there is no known complete filter media cartridge system that can accommodate selective regeneration of multiple cartridges in a single system to achieve continuous operation. Further the prior art systems are not compact and, as a result, not suitable for many vehicle applications. Moreover, existing filter media systems cannot be precisely controlled to provide customized continuous filtration. The energy consumption is very high in these prior systems.
Specifically, there are a number of products that address the problem of reducing diesel engine emissions through the use of Diesel Oxidation Catalysts (DOC). DOCs are usually constructed of a ceramic or metal substrate coated with a catalytic material. Although a DOC can reduce the Soluble Organic Fraction of the Particulate Matter, it has no effect on the carbon particles. Most systems based on catalytic oxidation achieve only in the order of 20-25% reduction in PM, the level presently approved by the EPA and which will soon be inadequate as new tougher standards are applied. Furthermore, as soot covers the surface of the catalytic converter, the catalyst quickly becomes ineffective which shortens the service life and degrades the performance of the system. Most of the systems rely on high exhaust temperature to initiate and maintain the regeneration, a factor that limits the useful range of these systems.
In the world market, many producers have emerged as key players, especially in Europe, taking advantage of the significant support from governments and diesel engine manufacturers. Currently, the European market is dominated by a few technologies, mainly variations of the ceramic substrates. The most prevalent mode of regeneration, unlike the USA market, is fuel additives. It is important to mention that the effect of such additives has not been thoroughly studied, but there are indications that perceived harmful side effects will impede their introduction to the USA market and might lead to limiting their wide spread use in Europe.
Diesel particulate filters available in today""s market are typically built on a ceramic substrate that traps soot by forcing the exhaust to flow through porous walls in a monolith. A catalyst is coated on the inside surface of the monolith. This lowers the soot combustion temperature, allowing the filter to regenerate at lower temperature than the ignition temperature of soot. An inherent limitation of such systems is that they rely on high exhaust temperatures and are practically inoperable at lower temperatures. For optimal performance, these systems require that the hot duty cycle of the engine be at least 20% of its operation, some system producers specify a hot duty cycle as high as 40-50% of the engine""s operation. In some driving conditions, it is difficult to maintain the necessary exhaust temperature required to regenerate this type of filter. Such a situation can cause excessive accumulation of particulate matter (soot overloading) and clogging of the filter and may later lead to uncontrolled combustion resulting in the destruction of the filter. To overcome this problem, some filters have installed electric heaters to maintain the necessary temperature for regeneration. Two regeneration strategies have developed in the market:
a. Regeneration while the engine is running, usually requiring large electric currents.
b. Regeneration while the engine is off. This is usually done after 8 engine hours, and requires plugging into an external power source, and is not convenient for normal driving conditions.
Another inherent limitation of the catalyzed ceramic filters is the fact that sulfur compounds in the Diesel fuel poison the catalysts needed to reduce the particulate matter emitted by Diesel engines.
In the prior art, it is also desirable to employ a nitrogen oxide (NOx) trap in addition to a particulate filter to improve the overall operation of the engine. Lean NO.sub.x traps operate cyclically. During the lean portion of the cycle (fill duration), NO.sub.x is adsorbed. After running lean for a period of time, the trapping efficiency becomes low and the trap must be regenerated. This is done by operating rich of stoichiometric. The hydrocarbons and CO emitted during rich operation causes the NO.sub.x to reduce to N.sub.2 and O.sub.2. The lean part of the cycle may typically last for one minute followed by the regeneration or purge part of the cycle for one second.
It is desirable that the transition between the fill and purge portions of the cycle be imperceptible to the driver. Accordingly, the prior art strategies provide for a relatively slow transition between the fill and purge portions of the cycle. Of the transitions that must occur, including fuel flow and spark changes, the most difficult transition is the manifold pressure change. The throttle (or other valve) must be closed rapidly to accomplish the lean to rich and rich to lean transition. Even after the throttle has attained the appropriate position, it takes a few cycles for the intake manifold to fill or to purge, depending on the transition. Thus, the transition occurs over a number of engine cycles. Because of the number of parameters which must be changed, it is a challenge to do this robustly and with no torque fluctuation. Furthermore, the ramping of the conditions which are required to get to and from the purge condition negatively impacts fuel economy. Alternatively, fuel may be separately injected into the NOx trap to supply the needed hydrocarbons for regeneration.
In view of the above, there is a demand for a low energy regenerable Diesel exhaust filter system which can successfully remove carbon, lube oil and unburned fuel particulates from the exhaust of a Diesel engine. It is also desirable for a filter system to be able to remove nitrogen oxide from the exhaust. It is also desirable that the regenerable filter system be compact and inexpensive to manufacture and use while being efficient in the field. It is desirable for a filter system to not impact the fuel economy of the engine while still providing an efficient filter system. Further, it is desirable that the filter system is reliable over long periods of time without maintenance while improving the overall performance and particle holding capacity, even at low differential pressure.
The present invention preserves the advantages of prior art electrically regenerated diesel particulate filter systems. In addition, it provides new advantages not found in currently available filter systems, and overcomes many disadvantages of such currently available filter systems.
The invention is generally directed to a novel and unique self-cleaning particle filter system with particular application in removing carbon, lube oil, unburned fuel particulates as well as nitrogen oxide from the exhaust of Diesel engines. The self-cleaning particle filter system of the present invention enables the inexpensive assembly, use and maintenance of a compact self-cleaning particle filter system for Diesel engines without detracting from the overall performance of the engine or the fuel economy thereof.
The preferred embodiment of the present invention includes a filter support plate with a plurality of cylindrical electrically regenerable filter media members connected thereto. A valve assembly includes a number of independently actuatable damper valves that correspond to a number of through holes in the filter support plate. When actuated, the damper valves limiting or reducing flow of air through a corresponding through hole and filter media member connected thereto. An outer housing is disposed about the valve assembly and filter media members to contain them in a compact package. A programmable computer control module shuts off the flow of air through a filter media member and selectively electrically regenerates it.
The filter system also preferably includes a NOx trap as well that takes advantage of the electrically regenerable particulate filter employed in the system. The NOx trap portion of the present invention may be in the form of a wash coat of the appropriate chemical composition, such as barium oxide) on the downstream side of the electrically regenerable filter media. As a result, the NOx trap is directly heated simulataneously while the filter media is being regenerated for removal of particulate matter trapped thereon. Also, hydrocarbons, in the form of unburned fuel, are supplied to the NOx trap layer on the filter media since it is in line with the exhaust which inherently traps excess hydrocarbons. Thus, the regeneration of the NOx layer and the removal of sulfur is facilitated without the need for the separate injection of hydrocarbons or separate heating source for the NOx trap.
In accordance with the method of the present invention, a filter support plate is provided with a plurality of through holes along with a number of cylindrical filter media members, each having a bottom closed end and a top open end. The cylindrical configuration has an outer surface defining an upstream side and an inner surface defining a downstream side with the top open end of each of the filter media members being connected to the filter support plate with the top open end of each of the filter media members in respective fluid communication with the through holes. A NOx trap chemical layer, such as barium oxide, is coated on the downstream side of the filter media. Alternatively, a separate NOx filter member, infused with barium oxide or the like, may be provide in communication with the downstream side of the filter media member. A valve assembly is provided with a number of damper valves connected thereto. Air, containing particulate matter therein, is passed through the filter media members so that particulate matter is collected in the filter media members. One of the damper valves is actuated into communication with its corresponding through hole thereby reducing flow of air through a corresponding filter media member connected thereto. Electricity is passed through the filter media member with reduced airflow therethrough. The filter media member, with reduced airflow therethrough, is regenerated. The NOx trap material, either directly coated to the filter media or in a separate filter member, is also regenerated with the assistance of the electrically generated heat as well as the hydrocarbons from the unburned fuel trapped by the filter media. To allow for resumed use of the now regenerated filter media member, its corresponding damper valve is actuated out of communication with its corresponding through hole thereby allowing full flow of air through the corresponding filter media member connected thereto.
It is therefore an object of the present invention to provide an improved Diesel exhaust filter system.
Another object of the present invention is to provide a Diesel exhaust filter cartridge with is electrically regenerated with a minimum amount of energy.
A further object of the present invention is to provide a Diesel exhaust filter system that also includes an integrated NOx trap that does not require the injection of additional hydrocarbons or separate heating supply.
It is a further object of the present invention to provide an exhaust filter, which is reliable over long periods of time without maintenance.
It is yet a further object of the present invention to provide a Diesel exhaust filter, which has improved overall performance and increased particle-holding capacity at low differential pressure.
It is another object of the present invention to provide a Diesel exhaust filter, which efficiently removes carbon, lube oil and unburned fuel particles from the exhaust of internal combustion engines.
It is yet a further object of the present invention to provide a low cost Diesel exhaust filter with improved manufacturability.
It is another object of the present invention to provide a filter cartridge system that achieves continuous operation.
A further object of the invention is to provide a filter cartridge system that is compact.
Another object of the present invention is to provide a filter cartridge system that is computer controlled to efficiently use an array of filter media cartridges.